One mechanism is provided with a screw including an external thread, with a nut arranged about the screw and including an internal thread, and with a plurality of longitudinal rollers engaging the external and internal threads of the screw and of the nut. In comparison with a ball screw mechanism, the main advantage of a roller screw mechanism is greater admissible load capacities.
A first type of roller screw mechanism includes rollers having an external thread engaging the external and internal threads of the screw and of the nut. The threads of the rollers and the thread of the nut have helix angles that are identical to each other and different to that of the thread of the screw such that, when the screw rotates in relation to the nut, the rollers rotate on themselves and roll about the screw without moving axially inside the nut. The rollers are rotationally guided parallel with the axis of the screw by teeth added on the nut and engaging teeth of said rollers. Such a mechanism is called a planetary roller screw.
A second type of roller screw mechanism has a similar operating principle but is different as a result of an inverted arrangement. The helix angles of the threads of the rollers, of the screw and of the nut are selected such that, when the screw rotates in relation to the nut, the rollers rotate on themselves about the screw and move axially in the nut. The rollers are rotationally guided parallel with the axis of the screw by teeth provided thereon and engaging teeth of said rollers. Such a mechanism is called an inverted planetary roller screw.
With the current design of roller screw mechanisms, the areas of contact of the rollers on the flanks of the thread of the screw and on the flanks of the thread of the nut are relatively reduced. This requires the load capacities of the roller screw mechanisms to be limited such as to prevent the occurrence of stress concentration.
The aim of the present invention is to overcome these disadvantages.
More particularly, the aim of the present invention is to provide a roller screw mechanism wherein, for a given diameter, the load capacity is increased.